Our studies on the virus-host cell interactions that result in the induction of leukemia continue. Emphasis is being placed on characterizing the biological and biochemical properties of the virus synthesized in tissue culture by various lines of murine erythroleukemia cells. Treatment with one of the many compounds which have been found to stimulate erythroid differentiation in these cultures also enhances virus synthesis. The virus produced, however, is attenuated. It will be compared to that of the highly leukemogenic strains in the attempt to determine the factor(s) responsible for the decreased leukemogenic activity. Cytological, immunological and molecular biological studies will also be carried out in an effort to elucidate the complex mechanisms involved in the induction and control of leukemia.